Industrially widely used as a method for producing methacrylic acid and methyl methacrylate is the ACH method (acetone cyanohydrin method), in which methacrylic acid and/or methyl methacrylate is produced from acetone and hydrocyanic acid (hydrogen cyanide).
However, hydrocyanic acid is highly toxic, and use thereof is undesirable.
Known as methods in which hydrocyanic acid is not used include, for example, a method in which isobutene or tertiary butyl alcohol is oxidized and a method in which propionic acid or a propionic acid ester is reacted with formaldehyde or the like.
However, isobutene is in a C4 fraction from ethylene plants or cracking gasoline plants, and there are limitations in procuring the compound for use as a material for methyl methacrylate production. In addition, it can be produced only in places equipped with a naphtha cracker.
In the method for production from propionic acid, the conversion to methyl methacrylate is low and the catalyst life is short. In addition, the Pd complex used as a catalyst for obtaining propionic acid from ethylene is not easy to synthesize and the stability thereof is problematic.
Meanwhile, also known is a method in which methacrylic acid or a methacrylic acid ester is obtained from a 1,1,1-trihalo-2-methyl-2-propanol. For example, a method is known in which 2-methoxy-2-methylpropanoic acid is obtained from 1,1,1-trichloro-2-methyl-2-propanol and the methyl ester thereof is obtained, and then subjected to alcohol elimination to obtain methyl methacrylate (Non-Patent Document 1).
In this method, however, it is necessary for obtaining 2-methoxy-2-methylpropanoic acid that a basic compound should be used in an amount at least 3 times by mole the amount of the starting-material alcohol. In addition, when methyl methacrylate is obtained from the methyl 2-methoxy-2-methylpropanoic acid, it is necessary that a phosphorus compound, metal chloride or the like should be used in an amount not less than an equivalent amount. The method is hence not considered to be an industrially practicable production method. Moreover, although the chlorine moiety in the starting material becomes a salt with the basic compound, it is difficult to effectively utilize the salt as such.
Known as another method for producing methacrylic acid is a method in which 2-chloro-2-methylpropanoic acid is heated at from 250° C. to 600° C. in the presence of a catalyst such as calcium chloride (Patent Document 1). Known as a method for producing methyl methacrylate is a method in which methyl 2-chloro-2-methylpropanoate is heated as a starting material at from 480° C. to 550° C. without a catalyst and then heated at from 250° C. to 350° C. in the presence of a dehydrohalogenation catalyst such as a metal chloride (Patent Document 2). The 2-chloro-2-methylpropanoic acid and the methyl 2-chloro-2-methylpropanoate can be produced, for example, by a method in which 2-bromo-2-methylpropanoic acid is obtained by reacting 1,1,1-tribromo-2-methyl-2-propanol with potassium hydroxide (Non-Patent Document 2).
In these methods, however, it is necessary to use a basic compound in an amount at least two times by mole the amount of the starting-material alcohol. In addition, the halogen salts obtained are difficult to be used effectively.